Methods for Identifying the Engineering Flexural Stress in FRP-Confined Concrete Columns

External fibre-reinforced polymer (FRP) jacketing has recently become increasingly popular for confining concrete in engineering applications. The elastic nature of the FRP jacket triggers a passive confinement field to the local dilation of the concrete core, resulting in a path dependency in its material response. Some research has been conducted to develop a flexural stress-strain model for FRP-confined concrete. However, the lack of an adequate stress identification method for flexure bodies has made it challenging to understand the material behaviour, resulting in an inaccurate outcome. This thesis proposes two stress identification methodologies to address this issue that enable the study of the flexural stress-strain relationship of any material. Although introducing novelty and generality, both methods are compatible with the modern engineering flexural theory of reinforced concrete (RC). Experimental studies based on the proposed methodologies were also made. The findings contribute to a better understanding of the behaviour of FRP-confined concrete under flexure and can facilitate more accurate predictions for engineering applications. 1. The first method presented builds upon an existing analytical approach for calculating the flexural stress of rectangular sections. As the original build suffers from limitations such as being inapplicable to non-rectangular sections and producing results with significant scattering, this thesis addresses these issues through rigorous mathematical derivation with analytical studies. Applying the proposed new method revealed the actual shape of the stress-strain relationship of FRP-confined concrete under eccentric loading for the first time. 2. The second method developed is a novel experimental approach considered entirely original. This method was established by carefully evaluating the well-known plane section hypothesis. Conducting tests using this method can reveal the local stress-strain response of the specimen.During a series of experimental studies, a non-unique characteristic was discovered in the test results, almost completely overturning existing studies’ previous conclusions on eccentrically loaded FRPconfined concrete in the literature. It suggests the local stress information is crucial for developing a realistic stress-strain model for FRP-confined concrete.